Microcontact printing is a printing technique that can be used, for example, to generate patterns of functionalizing molecules (that is, molecules that attach to a substrate surface or coated substrate surface via a chemical bond) to form a patterned self-assembled monolayer (SAM) (that is, a single layer of molecules that are attached, for example, by a chemical bond to a surface and that have adopted a preferred orientation with respect to that surface and even with respect to each other).
The basic method for microcontact printing SAMs involves applying an ink containing functionalizing molecules to a relief-patterned elastomeric stamp (for example, a poly(dimethylsiloxane) (PDMS) stamp) and then contacting the inked stamp to a substrate surface, usually a metal or metal oxide surface, so that SAMs form in the regions of contact between the stamp and the substrate. Typically, for inks comprising functionalizing molecules dissolved in a solvent, there are tradeoffs in printing performance and certain aspects of practical implementation that drive the selection of concentration for the molecules. In some circumstances, it is desirable to use the highest ink concentration possible because using higher ink concentrations can shorten print time, but the use of such high concentrations has presented practical challenges related to ink stability. In the past, stable ink formulations at high concentration have required the use of solvents (for example, hexane) that undesirably swell PDMS stamps.
The most commonly used inks for microcontact printing SAMs are ethanolic solutions of alkyl thiols. Unfortunately, however, alkyl thiols have a relatively low solubility and stability in ethanol. Inks comprising alkyl thiols in ethanol therefore typically contain a relatively low concentration of alkyl thiol.